Plutonium-239
Plutonium-239 (239Pu or Pu-239) is an isotope of plutonium. Plutonium-239 is the primary fissile isotope used for the production of nuclear weapons, although uranium-235 is also used for that purpose. Plutonium-239 is also one of the three main isotopes demonstrated usable as fuel in thermal spectrum nuclear reactors, along with uranium-235 and uranium-233. Plutonium-239 has a half-life of 24,110 years.[1]
This article is about an isotope of plutonium. For the film also known as The Half Life of Timofey Berezin, see Pu-239 (film).In nuclear power reactors[edit]
In any operating nuclear reactor containing 238U, some plutonium-239 will accumulate in the nuclear fuel.[5] Unlike reactors used to produce weapons-grade plutonium, commercial nuclear power reactors typically operate at a high burnup that allows a significant amount of plutonium to build up in irradiated reactor fuel. Plutonium-239 will be present both in the reactor core during operation and in spent nuclear fuel that has been removed from the reactor at the end of the fuel assembly's service life (typically several years). Spent nuclear fuel commonly contains about 0.8% plutonium-239.
Plutonium-239 present in reactor fuel can absorb neutrons and fission just as uranium-235 can. Since plutonium-239 is constantly being created in the reactor core during operation, the use of plutonium-239 as nuclear fuel in power plants can occur without reprocessing of spent fuel; the plutonium-239 is fissioned in the same fuel rods in which it is produced. Fissioning of plutonium-239 provides more than one-third of the total energy produced in a typical commercial nuclear power plant.[6] Reactor fuel would accumulate much more than 0.8% plutonium-239 during its service life if some plutonium-239 were not constantly being "burned off" by fissioning.
A small percentage of plutonium-239 can be deliberately added to fresh nuclear fuel. Such fuel is called MOX (mixed oxide) fuel, as it contains a mixture of uranium dioxide (UO2) and plutonium dioxide (PuO2). The addition of plutonium-239 reduces the need to enrich the uranium in the fuel.
Hazards[edit]
Plutonium-239 emits alpha particles to become uranium-235. As an alpha emitter, plutonium-239 is not particularly dangerous as an external radiation source, but if it is ingested or breathed in as dust it is very dangerous and carcinogenic. It has been estimated that a pound (454 grams) of plutonium inhaled as plutonium oxide dust could give cancer to two million people.[7] However, ingested plutonium is by far less dangerous as only a tiny fraction is absorbed in gastrointestinal tract;[8][9] 800 mg would be unlikely to cause a major health risk as far as radiation is concerned.[7] As a heavy metal, plutonium is also chemically toxic. See also Plutonium#Precautions.
Weapons grade plutonium (with greater than 90% 239Pu) is used to make nuclear weapons and has many advantages over other fissile material for that purpose. Lower proportions of 239Pu would make a reliable weapon design difficult or impossible; this is due to the spontaneous fission (and thus neutron production) of the undesirable 240Pu.